Our studies aim to determine the roles of the liver, kidney, mammary gland and placenta in vitamin A metabolism of fetal and neonatal sheep with various maternal intakes of vitamin A. Experiments will progress from evaluation of blood, liver and kidney responses in catheterized fetal and neonatal lambs given 3H-retinol to more advanced studies of responses to loading doses of vitamin A (which simulate therapy) given to the pregnant ewe and the neonatal lamb. Hepatic and renal arterial and venous catheterizations of the pregnant ewe and fetus, followed by 3H-retinol given orally, intravenously or intramuscularly will provide sequential quantitative data concerning vitamin A uptake, storage and mobilization. Analysis of free-3H-retinol, protein-bound-3H-retinol, 3H-retinyl esters and 3H-vitamin A-metabolites in blood, amniotic fluid, milk, tissues, urine and feces will help to determine factors controlling vitamin A utilization. Deconvolution and compartmental analysis will be employed to construct a mathematical model of the vitamin A system during pregnancy, fetal and neonatal life.